1. Field of the Invention
The present invention relates to a mandrel disposed on a packaging machine to form the bottom of a packaging container by folding and sealing a tubular package carton blank which is a thermoplastic coated paperboard and is provided with folding lines at both ends thereof.
2. Prior Art
Most beverages such as milk, juice, or the like are marketed in disposable packaging containers made of paperboard coated with a thin layer of plastic coating.
A beverage container having a gable top is formed from a tubular, half-completed carton blank which is generally square in cross section (see FIG. 5). The tubular carton blank includes four rectangular panels forming upstanding side walls divided by folding lines and two other portions which respectively form the top and bottom of the container. The top and bottom plates are folded about folding lines provided thereon to form respectively a gable top and a flat bottom.
The aforesaid tubular carton blank is folded into a tubular body configuration from a flat folded form. The carton blank is placed over a mandrel so that a foldable portion of the bottom of the tubular container is extruded from the top end of the mandrel. The mandrels are disposed radially on a mandrel wheel which rotates intermittently in a packaging container bottom forming apparatus. Then, the mandrel wheel rotates and pauses at the next step where heat is applied by hot air to soften and activate the thermoplastic coating on the foldable portion of the bottom of the paperboard container for heat-sealing. During the next movement of intermittent rotation, the foldable portion of the bottom is folded about the folding lines by means of a pair of folding devices. The folding devices each have two projecting folding fingers which are disposed on opposite sides of the circumferential route of the circular movement of the foldable portion of the bottom of the container. Then, the folded bottom is transferred through guides to the following step for sealing. At the sealing step, the bottom of the paperboard container which has been folded and prepared for sealing is compressed and sealed by heat-sealing between a flat top plate on the top of the mandrel and presser to form a sealed bottom. After the bottom is sealed, the completed container is transported to a removal station via an intermediate station wherein the bottom is cooled down to complete the sealing process before the container is removed from the removal step onto a conveyor line (See FIG. 4). Consequently, the half-finished tubular container, after being placed on the conveyor line, is filled with a beverage before the next step of folding and sealing the top portion thereof via heat sealing so as to provide a gable top.
The top of the mandrel is cooled with water so as to prevent the plastic coating on the body of the paperboard container from sticking due to the heat and pressure applied to the flat top plate disposed on top of the mandrel, while the heated and folded bottom is compressed between the outer end of the mandrel and the presser.
As shown in FIG. 7, the prior art mandrel has a cooling chamber 4' on the outer end of a mandrel body 2'. The cooling chamber 4' communicates with a flat top plate 3' so as to cool down the flat top plate 3' disposed above the top end of the mandrel 1'. As best seen in FIG. 9, which is a cross sectional view of the mandrel body taken along the line 9--9 of FIG. 7, the body of the mandrel 2' is H-shaped in cross section with the central member 2b' being of a certain thickness between a pair of crescent shaped side members 2a'. The end portions 5' of the mandrel fit inside the corners of the adjacent side panels C1 and C2 of the body of the tubular container C to correspond with the square configuration of the cross section of the body of the container. A pair of water-ways 6' are formed lengthwise in the central member 2b' and open to the aforesaid cooling chamber 4'. Cooling water flows from one of the waterways to the other via the cooling chamber 4'. Either the flat top plate 3' on top of the mandrel or the periphery of the cooling chamber 4' is formed to fit the inner wall of the tubular container C (see FIG. 8). The aforesaid cross sectional configuration of the mandrel is provided from the top end of the mandrel to the central area thereof to accept the tubular container C in full length thereon. In addition, the central member 2b' of the mandrel is provided with through holes 2c' for installing a stopper relative to the length of the tubular container employed.
As mentioned above, in the prior art the mandrel has waterways 6' provided in the mandrel body 2', so that cooling water flows through the cooling chamber 4' to cool down the bottom of the container which is sealed by heat-sealing. Accordingly, during the heat-sealing operation in which the folded bottom of the packaging container C is compressed and sealed between the flat top plate 3' on top of the mandrel and a pressing member 9 of the presser a pair of opposing side panels C1 and C1, and C2 and C2 of the tubular container C are directly cooled down by the crescent shaped side members 2a' of the mandrel body 2' which have been cooled by the cooling water and respectively fitted inside the corners formed by the adjacent side panels C1 and C2. Thus, moisture condensation occurs on the inner surfaces of the side panels C1 and C2. As a result, sanitary problems are created, for example impurities in the air are likely to be extracted from the water drops and remain on the inner surfaces of the aforesaid side panels. In addition, the mandrel 1' of the prior art is designed to be H-shaped in cross section and has recesses including through holes for installing a stopper and thus, cleaning is not facilitated.